Question: $-7st - 2su + 5s + 9 = 4t - 10$ Solve for $s$.
Combine constant terms on the right. $-7st - 2su + 5s + {9} = 4t - {10}$ $-7st - 2su + 5s = 4t - {19}$ Notice that all the terms on the left-hand side of the equation have $s$ in them. $-7{s}t - 2{s}u + 5{s} = 4t - 19$ Factor out the $s$ ${s} \cdot \left( -7t - 2u + 5 \right) = 4t - 19$ Isolate the $s$ $s \cdot \left( -{7t - 2u + 5} \right) = 4t - 19$ $s = \dfrac{ 4t - 19 }{ -{7t - 2u + 5} }$ We can simplify this by multiplying the top and bottom by $-1$. $s= \dfrac{-4t + 19}{7t + 2u - 5}$